1. Field of the Invention
This invention relates to reusable self locking fasteners and, in particular, relates to the method of applying metal patch to provide the self locking characteristics.
2. Description of the Relevant Art
A variety of self locking threaded fasteners have been utilized in the past. One type of prior art self locking fastener employed a plastic patch which utilized the elastic memory of the plastic material to maintain an adequate locking torque over a number of reuses of the fastener. While these plastic patch fasteners have been generally satisfactory in some applications, their usage has been somewhat limited or impaired by the relatively low modulus of elasticity of the plastic patch, causing the patch to provide only a limited locking torque; by their relatively poor performance in high temperature environments or in applications involving the use of certain organic fluids (e.g. solvents); and by the tendency of the plastic patch to cut. In particular, there has been heretofore a long-felt need for an improved self locking fastener having an improved reusability characteristic, a high locking torque and/or having the ability to perform well at high temperatures, and/or in the presence of organic fluids.
Another type of prior art self-locking fastener involved the use of a plated metallic patch harder than at least one of the corresponding threaded members. These types of hard metallic patch fasteners, such as may be seen in Bergere U.S. Pat. No. 3,552,467, operate by deforming at least one of the mating threaded members. While these fasteners are satisfactory for some uses if properly sized and if utilized with an easily deformable member, such as a nut, they will tend to permanently deform or destroy the threaded members if utilized with a relatively undeformable member such as a threaded engine block or if the patch is oversized.
Another type of prior art self-locking fastener utilized a relatively soft metallic coating on the threaded surface. This type of fastener such as is shown in Woodward (U.S. Pat No. 1,368,087) tended to provide relatively low locking torque and also tended to be relatively poor for repeated applications as the coating would tend to simply extrude after the first on-off cycle.
Somewhat more satisfactory metal patched prevailing torque fasteners were produced in Bedi (U.S. Pat. Nos. 3,818,525, 3,831,213 and 4,033,393) which disclosed spraying a selected portion of the threaded surface spraying with a molten metallic material to provide a relatively spongy or porous metallic patch over a relatively large, undefined threaded portion of the fastener.
In the Bedi invention, the metallic spray material comprises an alloy of copper and zinc which is applied to the fastener is a semi-molten particulate form with a flame spray apparatus. The fastener sequentially moves past the various pretreatment work stations and thereafter passes the metal spray work stations in a production line operation.
In the Bedi invention the fastener selected is usually a bolt member having a threaded shaft portion formed of a suitable steel and spongy metal patch material bonded to its shaft portion through the grit blasted porosity of the substrate and hot molten surface of the metal particles impinging the fastener surface at high velocity. The metal sprayed bolts must, then, be heat treated to sinter the porous metal patch deposit for an effective bond between the patch and the threaded surface. Without a final heat treatment process such as that described in U.S. Pat. Nos. 4,060,116 and 4,023,224 to Frailley, the metal patch applied using the Bedi method cannot be effectively and permanently adhered to the fastener.
Complete flame spray installation such as that described in U.S. Pat. No. 3,818,525 to Bedi requires specialized equipment to supply metallizing wire, controlled compressed air, fuel gas and oxygen, as well as appropriate safety equipment.
Flame spray guns suitable for carrying out the metal patching of bolts are commercially available for example from Metco, Inc. of Westbury Long Island, N.Y. While various flame spray guns are available from Metco, the type 12E is most suitable gun for this purpose. These guns are precision engineered for combustible gas spraying of the appropriate metallizing wire being fed into the spray nozzle at highly controlled rate.
Metallizing wires have to be specifically made for flame spray application. Oversized wires will often stick in the gun nozzle causing extreme wear of the gun parts and producing defective coatings due to erratic feeding. In addition to carefully controlling size, the metallizing wires must be free from kinks, bends and other physical imperfections for trouble-free flame spraying. Often the wires are treated with special lubricants to lessen nozzle wear and minimize fusing. These lubricants must be quality controlled to inhibit corrosion. Though coiling of the wire seems like a simple operation, coil diameter must be carefully controlled. The tendency to spiral, if not properly controlled, could cause down time and poor quality deposit quality.
In flame spray applications, the flame spray gun includes a fuel gas control unit which must include multiple stage regulator devices to monitor highly controlled combustion and hence flame spray deposit quality. In a flame spray gun, highest efficiency is obtained when the flow of fuel gas and oxygen is exactly balanced.
In addition typical flame spray guns require approximately 30 cubic feet of free air per minute at 65 psi. A pressure drop of 10 psi is required by the air regulator in order to achieve satisfactory wire feed rate to control the metal spray deposit thickness and quality.
Compressed air usually contains enough oil and moisture to weaken bonding strength of sprayed coatings. To prevent this an air compressor after cooler and appropriate filter must be used. Clean and dry quality compressed air is imperative to obtain a top quality flame spray deposit. The use of air flow meters are essential to monitor the consistency of the metal spray deposit.
In flame spray processes, it is very expensive to obtain at-will contour of the flame sprayed coating.
The flame spray process is limited because it cannot produce an at-will coating pattern without undergoing expensive masking and an additional machining step to contour the edge build up during spraying to produce acceptable self locking fastener. If the edge build up is not machined, the flame sprayed metal patch will tear off the substrate because of the mechanical bond nature of the flame sprayed metal patch.
In addition to being technically exacting, flame spraying can be hazardous. The process requires the use of combustible gases, containers and hoses under high pressure, and potentially irritating or toxic spray materials. Because of the nature of the materials used, special precautions must be observed when lighting the gun. Additional precautions must be taken during use because of the hot and hazardous nature of the stream of spray metal, the possibility of spray gun backfire and the fact that metal dust, having considerable calorific value, can be explosive. To minimize the danger of dust explosion resulting from flame spray, adequate ventilation must be provided. Because of the toxic nature of the dust, a water wash wet collector must be used in the exhaust gas stream to collect over sprayed metal powder.
Because of the nature of the equipment used in flame spray procedures, great care and caution must be observed in the work-place. Charged gas cylinders are potentially dangerous and hence have to be stored, used and moved under local, state, and federal regulations. No oil and grease can be used on oxygen equipment. Eye protection with specially designed, industrially accepted hardened green lenses must be used by the operators and those working near flame spray operations. Noise from metal spray combustion guns cannot exceed the maximum allowable limit as set by OSHA act of 1970. Any personnel in the immediate vicinity of such operations must wear hearing protection. Failure to heed to the prescribed precautions and safety measures while operating flame spray metallizing devices can result in accidents, causing property damage, personal injury or death.
According to the Bedi patents the process of metal deposition on a select threaded portion of the fastener requires the use of complicated equipment to atomize metallic materials through combustible flame spray guns. Because this process involves intricate controls to monitor the quality of wire, the quality of the compressed air and the mixture of combustible gases, the process can be extremely expensive to implement. Additionally significant amounts of metal are over sprayed and must be entrapped before escaping in to the environment. To say the least application of a metal patch according to the Bedi patents, is complicated, noisy, potentially hazardous, wasteful, expensive and must be followed by said Frailley heat treat process to be satisfactory.
Thus it is desirable to provide an improved reusable self-locking fastener which is capable of relatively high locking torques, is useable in relatively high temperatures and in organic fluid environments and is non-destructive to mating thread members with which it is associated. It is also desirable to provide an improved method of applying such a metal patch which is simple, economical, quiet, non-hazardous and non-wasteful. It is also desirable to provide self-locking fastener having improved resistance to high temperatures and organic fluids. It is also desirable to provide a superior interference thread self locking fastener over the prior mechanically bonded metal patch. It is also desirable to provide an improved reusable self-locking threaded fastener in which the filler metal is fused to select threads of the fastener in either its unheat treated or heat treated state.